And, as I've said in other threads, you CAN have an HDD APFS boot drive if you first format the HDD (or partition) to APFS and THEN install High Sierra on it.
I think the discussion about HDD and APFS is that the High Sierra install maybe doesn't offer the option for in-place boot drive conversion.
I think the discussion about HDD and APFS is that the High Sierra install maybe doesn't offer the option for in-place boot drive conversion.